This invention pertains to the design of reciprocating internal combustion engines for simplified manufacturing. More specifically, this invention pertains to an engine component design which permits the flexible manufacture of engines of similar but varying cylinder bore and piston stroke dimensions.
The modern four cycle, spark ignition, gasoline powered automobile engine is an elegant and increasingly fuel-efficient machine. Because of the wide ranging needs of vehicle owners, engines of widely different torque and power outputs must be produced. But each different engine size (or displacement) is of complicated construction and requires a large investment to design and manufacture.
In simplest terms, these internal combustion engines comprise a plurality of round pistons reciprocating within cylindrical bores and connected to a crankshaft with connecting rods. During a combustion pressure induced power stroke each piston applies torque to the crankshaft to provide the motive power of the engine. The torque and power delivered through the crankshaft is a function of the pressure surface area of the pistons and the length of their power strokes.
This assembly of pistons, connecting rods and crankshaft is housed in an engine block. The engine block defines the cylinders in which the pistons reciprocate and it locates and supports the crankshaft and connecting rods. It is open at the bottom. The pistons, connecting rods and crankshaft are assembled from the bottom of the block after inverting it. Finally the bottom of the block is closed with an oil pan. The engine block also contains engine coolant and lubricating oil passages. A cylinder head closes the tops of the cylinders in the block to define therein each respective combustion chamber with the enclosed piston head. The cylinder head also typically contains two air or fuel/air inlet ports and valves, two exhaust gas ports and valves, a spark plug and, often, a fuel injector. It also contains coolant and oil passages. Both the engine block and the cylinder head are metal castings of complex design. And each casting must be designed for the specified displacement of the engine.
As observed, it is very expensive to manufacture such engines with specifically designed and cast engine blocks and cylinder heads. It is foreseen that large savings could be realized in the manufacture of automobile engines if the design and manufacture of the engine block could be simplified. It is an object of this invention to provide a modular approach to making the engine structural components that contain the piston, connecting rod, and crankshaft assembly. It is a further object of the invention to separate the cylinder block portion of engine construction from the crankcase containing and assembling portion of the engine.
This invention focuses on the redesign of the engine block and oil pan portion of current automobile engines. Current production engines consist of a cylinder head and an engine block. These two components are bolted together with a head gasket in-between for sealing purposes. This configuration has been in production since internal combustion engines became available. The engine block itself is a big casting and requires a new design when either the bore diameter or stroke of the engine is changed. The production of a new engine block requires substantial tooling costs and its design delays new engine development.
This invention provides a new modularity in constructing automotive engines. In accordance with the invention, conceptually the current engine block is divided into two distinct sections: an upper cylinder bore block, which is preferably an extrusion, and a lower crankcase which will typically be a casting. The extruded cylinder block defines the cylinder bores and provides coolant passages around the cylinders. It has flat upper and lower surface portions for sealing purposes which will be described. The cast crankcase is shaped to contain and support the crankshaft and its bearing supports and bearing caps. It contains a closed bottom and side walls for these purposes. The side walls end in flat top surfaces also for a sealing function. A mid-plate separates the cylinder block and crankcase structures and provides openings for the connecting rods joining the pistons in the respective cylinder bores to the crankshaft in the crankcase.
The upper surface of the mid-plate has a gasket shaped to seal coolant in the cylinder block while the bottom surface of the mid-plate has another gasket to seal oil and blow-by gases in the crankcase. The mid-plate separator thus allows a single crankcase to be matched with varying sizes of cylinder bores for a family of engines.
The overall engine architecture then includes a conventional cylinder head and the extruded cylinder block and separate closed crankcase provided by this invention. A head gasket provides sealing between the cylinder head and upper surface of the cylinder block. Gaskets on both sides of the mid-plate provide sealing between the cylinder block and mid-plate and between the mid-plate and crankcase. These engine structural components from cylinder head to crankcase are bolted together by a set of long bolts into a suitably rigid and strong structure.
The open top of the crankcase permits easy placement of the crankshaft on its bearing supports and the positioning of the bearing caps on the journals of the crankshaft. Moreover, the continuous cylinder openings through the length of the extruded cylinder block and the cooperating holes in the mid-plate permit easy assembly of the connecting rods and pistons in and between the cylinder block and crankcase. Such placements and assembly can be accomplished without turning the engine over during this part of its construction. And the architecture requires no oil pan.
Generally, both the cylinder head and crankcase are cast parts. But the cylinder bore block is preferably an extrusion and can be cut to the length to meet the piston stroke needed. Extruded alloys are often stronger than cast alloys and, therefore, extrusions can sometimes be made smaller and lighter then the same part made by casting. Further, cylinder block extrusions can be made with lower cost tooling than cast blocks and can be extruded to close to net shape, thus requiring less machining.
With the cylinder bore block and crankcase being separated by the mid-plate, the sizes of the cylinder bores or lengths in a cylinder block are not rigidly tied to a specific crankcase or even a specific cylinder head. The selection of bore diameter and stroke may be limited by valve size, valve bridge width (e.g., minimum of 4 mm) or bore wall distance (e.g., minimum of 5.5 mm). Under these constraints, a modular engine construction as provided by this invention can accommodate approximately a 40% variation in engine displacement using the same cylinder head and crankcase. Thus, a modular engine architecture as provided herein can be utilized for designing and manufacturing a family of engines where the engine displacements vary within a range, for example 1.8 L, 2.0 L, and 2.2 L. For these three engines, a manufacturer could use the same cylinder head, crankcase, mid-plate and the gasket for lower mid-plate surface. Variations in engine displacement can be achieved by varying bore diameter, piston stroke, or a combination of both, in the extrusion of the cylinder block, which would be a commodity part. This family of engines could be produced on the same production line. The number of engines produced for each displacement could be quickly tuned to reflect the market needs for these engines.
The use of the extruded cylinder bore block and cast crankcase is also applicable in V-engine designs. In this embodiment, two extruded cylinder blocks would be bolted through two mid-plates to a single crankcase having wall sections to seal against the two V-legs formed by the cylinder blocks. The bearing caps would be shaped to accommodate this architecture.
In preferred embodiments of the invention, water cooling of the cylinder head and the cylinder block are managed separately. An electric water pump is employed with water flow circuits that enable the head and cylinder blocks to be cooled independent of engine speed and of each other. The object of this arrangement is to maintain uniform engine temperature at all speeds.
Just as different engine segments can be cooled with different coolant flow rates, lubricant flow to the cylinder head and the crankcase can also be separately controlled using an oil pump mounted outside the engine structure.
Other objects and advantages of the invention will become apparent from a detailed description of a preferred embodiment which follows.